Visualforce components are small, reusable pieces of functionality—think widgets, panels, user interface elements, that kind of thing—that you use in Visualforce page markup. You can use standard Visualforce components, and create your own custom components.
Please check the below link provided by salesforce help documentation of Visualforce page Components.
A Visualforce page can contain a mixture of HTML and Visualforce components.The HTML and component tags need to be well-formed, and all pages begin with the page component. For example, here is the most basic Visualforce page: <apex:page> </apex:page> Each component has a set of optional and required attributes, which provide additional information to the component. For example, the following attributes remove the sidebar and top header in a Visualforce page: <apex:page sidebar="false" showHeader="false"><!-- sidebar --> </apex:page>
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Rahulkumar
A Visualforce page can contain a mixture of HTML and Visualforce components.The HTML and component tags need to be well-formed, and all pages begin with the page component.
For example, here is the most basic Visualforce page:
<apex:page>
</apex:page>
Each component has a set of optional and required attributes, which provide additional information to the component. For example, the following attributes remove the sidebar and top header in a Visualforce page:
<apex:page sidebar="false" showHeader="false"><!-- sidebar -->
</apex:page>
Ex:
<apex:page sidebar="false" showHeader="false">
<apex:outputPanel layout="block" style="font-weight:bold"> <!-- outputPanel -->
VF Component.
</apex:outputPanel>
</apex:page>
Thanks
Find the below link for more information .
http://www.sfdcpoint.com/salesforce/custom-visualforce-component-example/
http://honeysalesforce.blogspot.in/p/visualforce-components.html